1. Field of the Invention
The present invention relates generally to dual fuel power generation systems employing one or more turbine engines. In another aspect, the invention concerns a dual fuel turbine system which can be powered by combusting natural gas and/or a gaseous fuel mixture of a light hydrocarbon and steam in the burner(s) of the turbine.
2. Description of the Prior Art
Coal-fired electrical power generation plants typically have an operating efficiency of about 30 to about 40 percent. In contrast, combined cycle electrical power plants, employing gas turbine engines and heat recovery, typically have an operating efficiency of about 40 to about 60 percent. Combined cycle power plants are also much less expensive to design and build than coal-fired plants. Because of these and other advantages, combined cycle power plants have been employed worldwide to provide electrical power for commercial and residential use. Similarly, the gas turbine or combined cycle plants can drive mechanical components like compressors.
To enhance the reliability of power generation, electrical utilities typically require combined cycle power plants to employ dual fuel systems for powering the turbine engine(s). Such dual fuel systems typically employ a gaseous fuel (e.g., natural gas) and a liquid fuel (e.g., distillate oils). The gaseous fuel is used to power the turbine under normal operating conditions, while the liquid fuel can be stored on site and used to power the turbine when the gaseous fuel is temporarily unavailable or when demand and/or price for the gaseous fuel is high. For example, when the weather turns cold the demand for natural gas as heating fuel and as fuel for electricity generation is very high. In such a situation, the liquid fuel can be used to power the turbine engine and generate electricity in a more reliable and/or cost-effective manner.
The dual fuel capability of combined cycle power plants requires additional construction, operation, and maintenance expenditures versus single fuel combined cycle power plants. For example, in dual fuel combined cycle power plants, both the gaseous fuel and the liquid fuel must have their own individual fuel control, distribution, and injection systems because the vastly different flow and combustion properties of the gaseous and liquid fuel make it virtually impossible to effectively control, distribute, and inject the fuels with the same fuel delivery system. Further, after the liquid fuel has been used to power the turbine engine, the liquid fuel delivery system must be thoroughly cleaned to prevent carbonaceous xe2x80x9cgum,xe2x80x9d or worse yet solid deposits, from building up in the liquid fuel delivery system.
It is an object of the present invention to provide a dual fuel power generation system which allows both a liquid fuel and a gaseous fuel to be delivered to a turbine engine via a common fuel delivery system.
It is a further object of the present invention to provide a dual fuel (i.e., liquid fuel and gaseous fuel) power generation system that transforms the liquid fuel into a gaseous fuel mixture having flow and combustion properties similar to those of the gaseous fuel.
It is still a further object of the present invention to provide a dual fuel turbine power generation system which allows the source of fuel powering the turbine to be readily switched back and forth between a liquid fuel source and a gaseous fuel source with minimal operational and maintenance expense.
It is yet a further object of the present invention to provide a dual fuel turbine power generation system which allows a gaseous fuel and a liquid fuel powering the turbine to be readily mixed in various proportions to provide a more cost-effective power generation system.
It should be understood that the above-listed objects are only exemplary, and not all the objects listed above need be accomplished by the invention described and claimed herein. Further objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiments, drawing figures, and appended claims.
Accordingly, in one embodiment of the present invention there is provided a power generation process comprising the steps of: (a) operating a turbine in a first mode wherein the turbine is powered by combusting a first gaseous fuel in a burner; and (b) operating the turbine in a second mode wherein the turbine is powered by combusting a second gaseous fuel in the burner, and the second gaseous fuel comprises a light hydrocarbon and steam.
In accordance with another embodiment of the present invention, there is provided a process for generating power using a gas turbine. The process generally comprises the steps of: (a) combusting natural gas in a burner of the gas turbine; and (b) combusting a steam-mixed fuel in the burner of the gas turbine, wherein the steam-mixed fuel consists essentially of a light hydrocarbon and steam.
In accordance with a further embodiment of the present invention, there is provided a dual fuel power generation system comprising a gaseous fuel source, a liquid fuel source, a steam source, a fuel mixing device, a turbine engine, and a fuel controller. The gaseous fuel source, liquid fuel source, and steam source are operable to provide gaseous fuel, liquid fuel, and steam, respectively. The fuel mixing device is fluidly coupled to the liquid fuel source and the steam source and is operable to mix the liquid fuel and the steam, thereby providing a steam-mixed fuel. The turbine engine is capable of being powered by combusting the gaseous fuel and the steam-mixed fuel, either individually or mixed. The fuel controller is fluidly coupled to the gaseous fuel source, the fuel mixing device, and the turbine engine and is operable to control the amount of the gaseous fuel and the amount of the steam-mixed fuel charged to the turbine engine.
In accordance with a still further embodiment of the present invention, there is provided a gaseous fuel composition comprising a gaseous mixture of a light hydrocarbon and steam. The gaseous mixture is above the dew point temperature and below the critical point of the mixture.